Machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery use one or more hydraulic cylinders to accomplish a variety of tasks. These cylinders are fluidly connected to a pump on the machine that provides pressurized fluid to chambers within the cylinders. As the pressurized fluid moves into or through the chambers, the pressure of the fluid acts on hydraulic surfaces of the chambers to effect movement of the cylinder and a connected tool. When the pressurized fluid is drained from the chambers it is returned to a low pressure sump on the machine. The fluid draining from the cylinder chambers to the sump has a pressure greater than the pressure of the fluid already within the sump. As a result, the higher pressure fluid draining into the sump contains potential energy that is wasted when directed to the low pressure sump, reducing efficiency of the hydraulic system.
An analogous reduction in efficiency may also occur in relation to a powertrain of a machine, used to actuate traction devices to propel a machine. Energy may be dissipated as heat and wasted when conventional brakes are applied to the powertrain to cause the machine to decelerate. Instead of using conventional brakes, a machine may be decelerated by transferring the kinetic energy via a powertrain to a motor via one or more electric motors.
One attempt at increasing the efficiency of a machine using hydraulic cylinders is described in U.S. Pat. No. 6,962,050 (the '050 patent) issued to Hiraki et al. The '050 patent discloses a hybrid machine including hydraulic cylinders for performing repetitive work against external loads. Hydraulic pumps are configured to supply hydraulic fluid to chambers of the hydraulic cylinders to extend the cylinders and perform work against external loads. The '050 patent discloses that the hydraulic cylinders may also contract under the force of external loads, e.g., when a truck bed lowers under the force of gravity, where the external loading may direct the hydraulic fluid in a reverse direction through the hydraulic pumps. The hydraulic fluid pressurized by the external loads may be used to drive electric motors connected to the pumps and generate electrical power.
Although the system of the '050 patent may provide a method for using hydraulic energy to generate electrical power, it fails to utilize other methods for generating electrical power. The '050 patent fails to simultaneously take advantage of using the mechanical energy of a powertrain and the hydraulic energy of a hydraulic system to maximize energy regeneration in a machine.
The present disclosure is directed to overcoming one or more of the shortcomings set forth above.